Louisiana State University LSU Digital Commons LSU Historical Dissertations and eses Graduate School 1962 Intersystem Crossing and Energy Transfer in Charge-Transfer Complexes. Nicholas D. Christodouleas Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: hps://digitalcommons.lsu.edu/gradschool_disstheses is Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and eses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. Recommended Citation Christodouleas, Nicholas D., "Intersystem Crossing and Energy Transfer in Charge-Transfer Complexes." (1962). LSU Historical Dissertations and eses. 770. hps://digitalcommons.lsu.edu/gradschool_disstheses/770
119
Embed
Intersystem Crossing and Energy Transfer in Charge ...
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Louisiana State UniversityLSU Digital Commons
LSU Historical Dissertations and Theses Graduate School
1962
Intersystem Crossing and Energy Transfer inCharge-Transfer Complexes.Nicholas D. ChristodouleasLouisiana State University and Agricultural & Mechanical College
Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses
This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion inLSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please [email protected].
Recommended CitationChristodouleas, Nicholas D., "Intersystem Crossing and Energy Transfer in Charge-Transfer Complexes." (1962). LSU HistoricalDissertations and Theses. 770.https://digitalcommons.lsu.edu/gradschool_disstheses/770
T h is d i s s e r t a t i o n h a s b e e n 6 3 -2 7 6 4m ic r o f i lm e d e x a c t ly a s r e c e iv e d
CH RIS T O D O U L E A S , N ic h o la s D ., 1 9 3 2 - IN T E R S Y S T E M CRO SSIN G AND E N E R G Y TRAN SF E R IN C H A R G E -T R A N S F E R C O M P L E X E S .
L o u is ia n a S ta te U n iv e r s i ty , P h .D ., 1962 C h e m is t r y , p h y s ic a l
University Microfilms, Inc., Ann Arbor, Michigan
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
INTERSYSTEM CROSSING AND ENERGY TRANSFER
IN CHARGE-TRANSFER COMPLEXES
A Dissertation
Submitted to the Graduate Faculty of the Louisiana State University and
Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of
Doctor of Philosophy
in
The Department of Chemistry
byNicholas D. Christodouleas
University of Athens (Greece), 1956 August, 1962
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
ACKNOWLEDGMENTS
I wish to express my gratitude to Dr. S. P. McGlynn, who directed
this research and who aided me patiently and understandingly.
I wish to express my appreciation to Professor H. Williams to
whom I owe my being at Louisiana State University.
Finally, I thank Dr. J. Nag-Chaudhuri for her valuable assistance
during the course, of this work.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
TABLE OF CONTENTS
CHAPTER PAGE
ACKNOWLEDGMENTS ....................................... ii
LIST OF TABLES....................................... v
LIST OF FIGURES....................................... vi
ABSTRACT............................................. viii
PART I (THEORETICAL)
A. ORGANIC MOLECULAR COMPLEXES ............................ 1
Introduction ......................................... 1The Origin of Charge-Transfer Theory ................. 2Formulation of the Theory ........................... 3Resonance in the Charge-Transfer Complexes ........... 5Polarization of Charga-Transfer Transition........... 8Charge-Transfer Ground State Interaction and Intensityof Charge-Transfer Ba n d ........................... 9
Paths of Excitation and Energy distribution.......... 13The Perturbation of the Donor-Triplct State in theCharge-Transfer Complexes ......................... 15
B. THEORETICAL CONSIDERATIONS OF SPIN-ORBITAL COUPLINGINTERACTION......................................... 17
PART II (RESULTS OF THE PRESENT RESEARCH)
A. ELECTRONIC ABSORPTION SPECTRA OF CHARGE-TRANSFER COMPLEXESOF NAPHTHALENE WITH HEAVY ATOM CONTAINING ACCEPTORS . . . 22
Introduction ......................................... 22Experimental ......................................... 23Results and Discussion . 2 3
Stability Constants (Kx) and Electronegativity of theAcceptors....................................... 24
Comparison of the Values of Molar Absorption Coefficients Ec and Oscillator Strengths F ' s .......... 24
Free Energy of Formation of Naphthalene Tetrahalo-phthalic Anhydride Complexes ................... 27
Correlation of Ec or Ex and Kx of the Complexes with _^max of C-T Band............................. 27
iii
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
CHAPTER PAGE
Geometrical Structures of C-T Complexes ............ 28Width of Complex Absorption Bands ................. 29The Effect of Solvent on the Stability Constants of
the Complexes................................... 29
B. INTERSYSTEM CROSSING IN CHARGE-TRANSFER COMPLEXES OFNAPHTHALENE WITH HEAVY ATOM CONTAINING ACCEPTORS . . . . 40
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
L IS T OF TABLES
TABLE
I. Spectrophotometric and Thermodynamic Values for Some Naphthalene Complexes
II. Molar Absorption Coefficient £e of Some Naphthalene Complexes Calculated on the Basis of Molarity of the Complex
III. Spectrophotometric and Thermodynamic Values for Some Naphthalene Complexes in Different Solvents
IV. Fluorescence and Phosphorescence Intensities in the Total Emission Spectra of Naphthalene-TCPA Complex
V. Fluorescence and Phosphorescence Intensities in the Total Emission Spectra of Naphthalene-TBPA System
VI. Fluorescence and Phosphorescence Intensities in the Total Emission Spectra of Naphthalene-TIPA Complex
VII. Fluorescence and Phosphorescence Intensities in the Total Emission Spectra of Naphthalene-sym-TNB
VIII. Comparison of Fluorescence and Phosphorescence Intensities in the Total Emission Spectra of Naphthalene with TCPA, TBPA and TIPA
IX. Relative Fluorescence and Phosphorescence Intensities of Naphthalene-TCPA Measured with the Aminco-Keirs Spectrophotometer
X. Relative Fluorescence and Phosphorescence Intensities of Acenaphthalene-sym-TNB Measured with the Aminco-Keirs Spectrophotometer
XI. Relative Fluorescence and Phosphorescence Intensities of Phenanthrene-sym-TNB Measured with the Aminco-Keirs Spectrophotometer
XII. Comparison of v^max (Absorption) and ^max (Emission) for Some C-T Complexes
v
PAGE
30
31
33
51
52
53
54
55
64
65
66
81
R ep ro d u ced w ith p erm iss io n o f th e cop yrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
L IS T OF FIGURES
FIGURE
1.
2 .
3.
4.
5.
6 .
7.
8.
9.
10.
11.
12.
13.
14.
General Potential Energy Diagram of Charge-Transfer Complexes
Plot of Molar Absorption Coefficient £ .* vs. Wave Number of Absorption in the Complexes: Naphthalene-TCPA, Naphthalene-TBPA, Naphthalene-TIPA and Naphthalene-2,4,7 TN-Fluorenone
Molar Absorption Coefficients £<e vs. Wave Numbers of Absorption for the Complexes in Other Than Chloroform Solvents
Plot of Molar Absorption Coefficient^* vs. Peak Wave Length of the C-T Band
Plot of Stability Constants vs. Peak Wave Length of the C-T Bands of the Naphthalene Complexes in Chloroform Solution
Charge-Transfer Spectrum of Naphthalene-2,4,7 TN- Fluorenone at Three Different Temperatures
Molar Absorption Coefficients of (1) Naphthalene in iso-Octane, (2) TCPA in Chloroform and (3) Naphthalene-TC^Jl in Chloroform
Total Emission of Pure Naphthalene and Naphthalene-sym-TNB
Total Emission Spectra of Three Solutions of Naphthalene Complex
Plot of C f? p/ <^f vs. Concentration of TCPA
Plot of ^ p / ^ f vs. Concentration of TBPA
Total Emission Spectra of Naphthalene with Equimolar Amounts of TCPA, TBPA and TIPA
Plot of ^ p / (j?f vs. (SOCF)^ of the Halogens
Total Emission Spectra of Phenanthrene-sym-TNB Complex
vi
PAGE
7
35
36
37
38
39
56
57
58
59
60
61
62
67
R ep ro d u ced with p erm issio n o f th e cop yrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
FIGURE PAGE
15. Emission and Absorption of Anthracene-2,4,7 TN-FluorenoneComplex 73
16. Emission and Absorption of Anthracene-sym-TNB Complex 74
17. Emission and Absorption of Anthracene-TCPA Complex 75
18. Emission and Absorption of Tetraphene-sym-TNB Complex 76
19. Emission and Absorption of Coronene-sym-TNB Complex 77
20. Emission and Absorption of 3, 4 Benzotetraphene-sym-TNBComplex 78
21. Emission and Absorption of Phenanthrene-sym-TNB Complex 79
22. Plot of ^max (Absorption) and ^ max (Emissioi) of SomeCharge-Transfer Complexes 80
vii
R ep ro d u ced with p erm issio n o f th e cop yrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
ABSTRACT
A. The charge-transfer spectra of Naphthalene with a number of
organic acceptors such as Tetrachlorophthalic anhydride, Tetrabromo-
phthalic anhydride, Tetraiodophthalic anhydride, etc., were investigated.
Stability constants of complex formation and other thermodynamic and
spectroscopic data are presented.
From the positions of the maxima of charge-transfer bands and by
comparison of the values of stability constants, it is concluded that
Tetraiodophthalic anhydride is the strongest electron-acceptor in the
Tetrahalophthalic anhydride series. A linear relationship between max
and absorption coefficient has been found in the Tetrahalophthalic
anhydride series. The concept of "contact C-T" absorption is introduced
and is used, by means of a simple quantum mechanical formulation, for the
explanation of the variation of oscillator's strengths of C-T absorption
in the Tetrahalophthalic anhydride series as compared with the variation
of stability constants.
Some comments on the influence of solvent upon the stability
constants, on the geometrical structure of the complexes, and on the width
of the charge-transfer bands are given.
B. Intersystem crossing between the lowest triplet state and the
first excited singlet state of Naphthalene increases considerably by
complexing it with various heavy atom containing acceptors. This can
be deduced by comparing the Phosphorescence intensity of a certain wave
viii
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
length peak to that of Fluorescence in the total emission spectra of
charge-transfer complexes of Naphthalene with Tetrachlorophthalic
intensity of Phosphorescence and Sym-Trinitrobenzene. The ratio: intensity of Fluorescence
has been found to depend on the concentration of acceptor for a certain
amount of Naphthalene as well as on the nature of the heavy atom in the
acceptor. It is believed that an intermolecular spin orbital coupling
perturbation is involved operating by means of complexation. The role
of the G-T state as an intermediate in the energy transfer is examined.
C. The C-T emission in a series of complexes of sym-TNB,
Tetrachlorophthalic anhydride and 2,4,7-Trinitrofluorenone with certain
polycyclic aromatics at room temperature and in the crystalline state
was investigated. It has been found that C-T emission under the above
mentioned conditions exists and is characterized by a symmetry corres
pondence between the maximum wave length of absorption (^max) and that
of emission.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
CHAPTER A
ORGANIC MOLECULAR COMPLEXES
Introduction
Organic molecular complexation is a well-known phenomenon since the
early days of the development of organic aromatic chemistry. Its initial
importance consisted primarily in the scientific curiosity of the synthetic
organic chemist, and later in its analytical use in spot test procedures'*' and2 3 4in the spectrophotometric determination of adduct molecular weights. ’ ’
The theory of formation of organic molecular complexes was a matter
of controversy in the various stages of its development. We shall not
attempt to consider here the theories which have been proposed, nor shall
we try to justify the reasons why specific explanations have failed. This
is a matter of historical interest which is well delineated in the numerous5 6books and review papers published on the subject. ’
. Feigl, Spot Tests in Organic Analysis, Elsevier Publishing Co., New York, 1958, 5th Edition, p. 327.
2K. J. Cunningham, W. Dawson and F. S. Spring, J. Chem. Soc., 73, 4437 (1951).
3Yu. N. Sheinker and B. M. Golovner, Izvest. Akad. Nauk. S4_S.R.,
ser. Fiz. _17, 681 (1953).4V. I. Siele and J. B. Picard, Appl. Spectroscopy 12, 8 (1949).5 ii iiG. Briegleb, Zwischenmolekulare Krafte, G. Braun, Karlsruhe,
R ep ro d u ced w ith p erm iss io n o f th e cop yrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
2
One point, however, seems to us relevant: the theories of valence
were developed separately in the two branches of chemical science (organic
and inorganic) with no strong bond between them. It was natural then
that any kind of generalization between the secluded theories would be
ambiguous and uncertain. However, as a theoretical background of the
discussions related to the experimental work which has been done by us
we shall outline the most advanced and consistent theory, namely thei, «. c f M i r , 7,8,9,10,11,12,13,14charge-transfer theory of Mulliken.
The Origin of Charge-Transfer Theory
The origin of C-T theory, it might be said, is found in electronic
absorption spectroscopy. It is found in the impossibility of explaining
intense electronic transitions due to complex formation by means of classi
cal and/or dispersion forces. Indeed, iodine in the gaseous phase does not
absorb above 200QA, yet when dissolved in Benzene a strong absorption band
appears with Jmax = 2970 A. This band cannot be explained on the basis of
dispersion forces because the first dispersion force excited state lies at
^R. S. Mulliken, J. Am. Chem. Soc., 72, 600 (1950).
8Ibid., 72, 4493 (1950).
9J. Chem. Phys■, 19, 514 (1951).
10J. Am. Chem. Soc., 74, 801 (1952).
Phys. Chem., 1)6, 801 (1952).
12J. Chem. Phys., 51, 341 (1951).
13J. Chem. Phys., 23, 397 (1955).
^Rec. trav. chim., J5_, 845 (1956).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
1 smuch too high energies, ca. 19 ev above ground state of the complex. J
In addition to this, attempts to interpret the observed absorptions of
this and other complex systems as due to intensified weak transitions in
either component of the system failed^’ ^ until a more general inter
pretation of this characteristic absorption band in terms of donor acceptor19 20 21 22 23interaction was given. 5 ’ ’ ’ This was finally achieved in 1952.
Formulation of the Theory
The basis of quantum mechanical treatment of donor acceptor inter
action is the description of the wave functions of the system as linear
combinations of functions corresponding to the various states of separated
donor and separated acceptor. According to this treatment the ground
state wave function of the complex may be written:
' l / £ ( D ,A) » a f t , (DA) + (, l / f (D+,A“) 1
In general D or A may be molecules, molecule-ions, or atom-ions, but with
the restriction that they are both in their totally symmetric ground state.
^S. H. Hastings, J. L. Franklin, J. C. Schiller and F. A. Matsen,J. Am. Chem. Soc., 75, 2900 (1953).
16N. S. Bayliss, Nature, 163, 764 (1949).
^N. W. Blake, H. Winston and J. Patterson, J. Am. Chem. Soc., 73, 4437 (1951).
18J. S. Ham, J. R. Platt and H. McConnell, J. Chem. Phys., 19, 1301
21J. Weiss, J. Chem. Soc., 1942, 245 (1954).22R. B. Woodward, J. Am. Chem. Soc., 64, 3058 (1942).23W. Brackmann, Rec. tray, chim., 68, 147 (1949).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
"{j/^ corresponds to the state in which the binding of the two components
is due to classical intermolecular forces, such as dipole-dipole, ion-
dipole, ion-induced dipole interactions, etc., to hydrogen bonding or to
effects of higher order such as Longon dispersion forces and is called
the no-bond wave function. I f s is called the dative-bond wave function
and corresponds to the structure which results from the transfer of one
electron from the donor to the acceptor. is characterized by a minor
degree of covalency and by electrostatic forces in addition to the above
mentioned forces. The electrostatic forces in are particularly dominant
if A and D are neutral species. Eq. 1 may be extended to include the reversej_ — ™ "hto (D ,A ) transfer; namely (D ,A ) as in the case of self complexes or
when (D) is a weak base and (A) a weak acid, as follows:
n f c (D,A) - a ^ (DA) + b l f ^ (D+A~) + cj^ (D“A+) 2
The relative values of coefficients a,b and c is a measure of the
contributions which the structures % (DA), l f \ (D+A“), and ^ (D"A+)
confer to the ground state D,A). Usually a>b^>c and eq. 2 is reduced
to the more simplified eq. 1.
On the basis of eq. 1 the ground state energy E can be estimated
using the Ritz Variation procedure. The result is:
(Wo - E) (WL - E) = (Hq1 - ES)2 3
Where: WQ T, WL = f a f f dT and
dT■fyi # V
H is the total Hamiltonian of the entire set of nuclei D and A in the
complex system. Since a^b, it is permissible to substitute W- for E in
all terms except (Wq ” E). Then eq. 3 is reduced to:
E - WQ - (Hq1 - WQS)2/ (Wj_ - W0) 4
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
5
with b/a = - (HQ1 - SW^)/ (W^ - Wq) according to the second order
perturbation theory.
The assumption that Ip// is normalized permits evaluation of a2 2 jand b individually since a + 2abS + b = 1 . The excited state wave
function (by analogy with the usual resonance theory) is:
(D,A) = a* lj^1 (dV) - b* ^ 0 (DA) 5
with a*=a, b*Cb. The normalization procedure gives
a*2 - 2a*b*S + b*2 = i 6and the approximation of the second order perturbation theory
WE ^ W1 + (H01 " SW1)2/ (W1 “ V 7with b*/a* = - (H oi ” SW^)/ (W- - W q ). It is interesting to note that
T^o.A) is primarily of no-bond character and l ^ E (D,A) is of ionic
character since a2» b . The transition is called the inter-
molecular charge-transfer transition, and its absolute intensity can be
approximately computed.
Resonance in the Charge-Transfer Complexes
The stability of the C-T complexes in the ground state is due to
the resonance between the no-bond structure (DA) and the ionic struc- + ™ture (D, A ). This is clarified by an illustrative diagram Fig: 1
showing the variation of potential energy of the system as a function
of the intermolecular distance DA. The forces operative in the no
bond structure are the above mentioned classical ones, such as dispersion
forces, dipole-dipole, hydrogen bonding, etc., which may lead to small
bonding. At small intermolecular distances a small repulsion will
arise due to the closed shell repulsion forces. Such a situation is
represented by curve E,. In the dative structure (D+ ,A ) the
R ep ro d u ced with p erm iss io n o f th e copyright ow n er. Further reproduction prohibited w ithout p erm issio n .
6
dominant force is the Coulombic electrostatic attraction. However, a
small covalent bonding between the two electrons situated on the two
components exists and this covalency makes (D*A ) neither a free radical
nor a biradical, except for large interatomic distances where the Hund
interaction of spin is small.
The intervention of resonance causes mutual replusion of curves
and Eq to produce and Eg. It can be easily seen that the C-T
absorption energy will be determined by the distance of the two minima
of curves Eg and E^f. An essential requirement for resonance is that Hq^
and S o l non zero. Since H has the total symmetry of the complex,
this requires t h a t d T be non zero. From the point of view of
group theory this implies that ^ 0 and ^/l belong to the same represen
tation of the symmetry point-group defined by the geometry of the complex.
i f 0 and ^ must also be of the same spin-type unless there are heavy
atoms in the molecules. Now in the structure D*~A , D+ has the symmetry
of the hole in its highest occupied molecular orbital, whereas A has
the symmetry of its lowest unfilled molecular orbital. If these orbitals
are designated by and then the product / f D ( k must contain
the totally symmetric representation. f a signifies the representation
of In addition, ^ dT = maximum corresponds to the
energetically most favorable orientation of the molecules in the complex.
This is the so-called Orientation and Overlap Principle. The discussion
of this principle is not within our range of interest.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
7
5i2 *'DA'
.D. A,e"
- D'A
a TE
0+0
h*
1E0
Figure 1
On the left are plotted the potential energy curves as a function
of the intermolecular distance Y da. Curves Eq and E- represent the
energies of the structures IpO (DA) and ( D + ,A- ). Resonance repulsion
of Eq and E^ has produced E^ and Eg.
On the right the important energy quantities determing the ground
state stabilization energy, the C-T energy, etc., are diagrammed . The
symbols are the same as those used in the text.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
8
It is found experimentally in a series of complexes of the same
acceptor with different donors that is a linear function of f p . In
other words, a plot of i f ' v s . f p t o x the C-T band peak yields a straight
line. From Fig: 1 we can easily deduce the following relationship between
the C-T energy and the other energy characteristics of the system, namely:
k / " = ( To - E - E + p c ') - (E + <*' ) 8A C
Eq. 8 complies with the above mentioned experimental relationship if the/
quantity (Ec - Eq +D(- 0 ( ) is independent of the nature of the donor.
This is a surprising conclusion the generality of which has diminished
after the observation that deviations do exist, especially in strong24 25
complexes. For example in H ' I2 and (C2 Hg ^ S ' I2.
Polarization of Charge-Transfer Transition
Let us consider for simplicity a one electron system as our donor
acceptor interaction system. The ground state of this system has an
electron in a donor orbital and the C-T state an electron in an
acceptor orbital ^a. That is:
(DA) = ^d 9
2 ( D V ) = ? &
However, on account of the interaction of donor-acceptor states under the
influence of the Hamiltonian, a new ground state d and a new excited
state ^ a! arise. The intensity of the C-T band is proportional to the
square of the transition dipole moment between cl and fa.. The C-T state
is said to be polarized along the intermolecular axis because the dipole
24S. Nagakura, J. Am. Chem. Soc., 80, 520 (1958).25M. Good, A. Major, J. Nag-Chaudhuri, and S. P. McGlynn, J. Am.
Chem. Soc., 83, 4329 (1961).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
9
moment of the electron distribution is directed along this axis so that
the component of the light whose electric vector is parallel to the
intermolecular axis is absorbed. Nakamoto's observation that the first
absorption band of the quinhydrone-type complexes, such as Chloranil-
Hexamethylbenzene, is polarized in a plane perpendicular to the plane of
the two components is direct evidence that these bands have C-T
character.
Charge-Transfer Ground State Interaction and Intensity of the Charge-
Transfer Band
Let us consider the one electron system in which the ground state
and C-T state wave functions are written as:
Where: al donor, and i is the
eigenfunction of the acceptor negative ion. The total Hamiltonian H of
the system must include the electrostatic potential of the donor positive
Now as a result of the interaction between the donor and acceptor the
26
9
ion the potential and the kinetic energy
operator T as follows:
From ou t follows:
11
10
ground and the C-T state will not be but:
12
^K. Nakamoto, J. Am. Chem. Soc., 74, 1739 (1952).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
10
ft' - f t + J d a ftd
The coefficients ad and _/]da can be determined by the perturbation
theory and the result is:
Had - Sad Hdd%-^da = Ea - Ed 13b
ad = Ed - Ea 13a
Had - Sad Haa
Where:
Had = dT and Sad - f t a f t dT
From eqs. 10, 11 and 13 we can easily obtain:
0 Vad (A) - Sad Vdd (A)./I ad = Ed - Ea«y| ad = Ed - Ea 14a
a y k . (D+ ) - SadV'aa _£A2 jlda Ea - Ed 14b
Where: V a d (D+) is the energy associated with the charge distribution
f t ft in the field w ). Making use of the normalized overlap
density C f a t f h / s ad we obtain:
/ \ I I % Cpj l ad (Ed - Ea) = Sad Sad - Jc-d2 V(A) dT = SadWad (A)
15a
ft / yaXd,,, \/ + +j \ da (Ea - Ed) = Sad I I Sad - Ta V(D ) dT=SadWda (D )
15b
It is interesting to note the inequality: _y|ad da. The
integrals W represent the interaction of the electrostatic fields of
acceptor or donor positive ion with a charge distribution which inte
grates to zero. The value of Wda (D+) or Wad (A) will depend on the
position of the charge distribution in the field V (D*") or \/(A) and
are functions of the magnitude of ^ d relative to fta If d is
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
11
small compared with fta, then the center of density ftd fta is near D+
and the energy (D ) is large compared with VVad (A). The opposite
is the case if ^a is small compared with ftd.
In general we expect that ft < f t and consequently
Wda (D+) » Wad (A). 16
This prediction is supported by the fact that W ) falls off more
slowly than V (A ). \/(A ) is zero outside the electron cloud of A.
From the expression 16 it follows that / J da j a d j which means
that there is more ground state introduced into the C-T state than C-T
state introduced into the ground state. If Wad (A) is approximately
taken equal to zero, then
ft' = ft, ft a 1 = fta - Sad ftd 17
because the orthogonality relationship between ftd' and fta' implies
that
J^da + ^ a d = - Sad. 18
The stabilization of the ground state is
- ^Ed = ^ 2ad (Ea - Ed)
and the destabilization of the C-T state is
^ Ea = J^da (Ea - Ed). 2.0
Now let us calculate the transition dipole moment Md'a' of the C-T band
and see what factors influence it.
By definition:
Md'a' = f ? d ' M fta'dT 21
Considering that
ft' - ft + J)ad ft. f t ’ = fta +^da tyd and
^da -t- ad = - Sad
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
12
We get
Md'a = „^ad (Maa - Mdd) + (Mda - Sad Mdd) + a term in 22
Eq. 22 indicated that there are two contributions to the dipole
moment. The first is proportional to the dipole moment of the trans
ferred electron and the resulting hole, and it is related to the
stabilization of the ground state through the coefficient ^ad. The
second contribution should be viewed as the factor responsible for the
so-called contact C-T absorption which is observed if no stabilization
of the ground state occurs. If the second term is written in such a
way as to include the normalized overlap density we can get an idea of
how this term changes in relation to the first one, namely:
f [:.&_& 6*1 - -i J L Sad - r d rMda - Sad Mdd = Sad e l L- Sad - 'j d_J r d r 23
Comparing eqs. 15 and 22 we conclude that the factors which make the
first term small ( ^ d small compared with ^a) make the second term
small also.
There is, however, the following difference; it is not possible
to say definitely that if the first term in 22 is zero that the second
term will also be zero. What we can say is that the factors which
make the one small make the other small also. And here lies the condi
tion of contact charge-transfer. If Orgel and Mulliken's interpretation
is correct, it is necessary that when ^ad becomes zero, the dipole
moment of Qfd 9 VSad - does not become zero. Such is the
case when the C-T band is polarized in a plane perpendicular to the
direction of charge-transfer. In order to get a practical feeling of
eq. 22 we shall simplify it further by using the following equation:
Mda - Sad Mdd = e Sad 24
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
13
Where:
Y-d = /ft 7 f t dT 25a
f DA “/ ft ft <? a dT/Sad 25bIf we assume that this is the only term contributing to the expression
27of dipole moment, then:
Md'a1 = - e Sad 26
Where:
is the separation of donor and acceptor charge centers in1 DAcontact. On the other hand the Oscillator strangth of C-T transitions
27is given by the following expression:_9 f -
(Experimental) = 4.32 x 10 J E dv^ 27a
(Experimental) = 1.35 x 10 Emax ( )/"max - Y "%) 27b
(Theoretical) = 4.704 x 10 V -max M^d'a' 27c
Where:
V* is the frequency in cm and E the molar absorption coeffi
cient, \Z"max and Emax are the frequency and molar absorption coeffi
cient respectively at peak absorption, and V" % is the half width of the28absorption band. Combining eqs. 26 and 27c we obtain:
f E d\ = 2530 S^ad . r^da (A^) V^max (cm ) 28
The average molar absorption coefficient will be:
E = 20.000 S2da r2DA 29
Paths of Excitation and Energy Distribution
In the previous section we have mentioned that the condition of
27S. P. McGlynn, Chem. Revs., 58, 1113 (1958).28D. S. McClure, Radiation Research Suppl., 3 , 218 (i960).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
14
contact C-T absorption is that the following relationships apply
simultaneously.
^ a d (maa - Mdd) = 0 30a
(Mda - Sad Mdd) 0 30b
But this imposes a strain on the theory since both quantities vary uni-
directionally. If we assume, however, that it is not the ground state
only that mixes with the C-T state but also the donor excited state this
strain is reduced appreciably. Under these conditions the ground and
C-T state wave functions will be (using the one electron approximation):
C f d' = 6>d + J|ad t y a 31a
Cfa' - (fa . : J i da * fd + -Ai*a t y d * 31b
Where fy d * is the excited donor-wave function, the dipole moment of the
transition ^ f d ' - * t y a ' is:
Md'a1 = Mda + _^ad Maa +_^da Mdd + _^d*a Mdd* 32
From the orthogonality relationship between ^d' and ^ a ' we get «^ad +
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
TABLE II
MOLAR ABSORPTION COEFFICIENT OF SOME NAPHTHALENE COMPLEXES CALCULATED ON THE BASIS OF MOLARITY OF THE COMPLEX
Donor Solvent Ec /Ecdy- f = 4.32 x 10* fEcdp-
Tetrachloro-phthalic Chloroform 1.0 X 103 3.28 x 106 0.014
Anhydride2 n-Hep tane +
1 ether 0.91 x 103 2.94 x 106 0.013
Tetrabromo-phthalic Chloroform 0.91 x 103 2.92 x 106 0.012
Anhydride n“c7H16 1.0 x 103 2.76 x 106 0.011
Tetraiodo-phthalic Chloroform 0.42 x 103 0.93 x 106 0.004
Anhydride Ec 20°c = 0.45 Ec 31°c = 0.39
Sym-TNB n"c7Hl6 1.33 x 103 5.70 x 106 0.025
3 2
R ep ro d u ced with p erm issio n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
TABLE III
SPECTRGPHOTOMETRIC AND THERMODYNAMIC VALUES FOR SOME NAPHTHALENE COMPLEXES IN DIFFERENT SOLVENTS
Acceptor SolventTemp. °C Ec Kx
- A fKcal/mole
- AhKcal/mole
- AS e .u.
Sym-TNB n-Heptane 50 3600 1.33 X 103 13.4 1.68II ii 32 3600 1.33 X 103 19.8 1.82 4.26II ii 7 3600 1.33 X 103 24.0 1.7711 ii 20* 3600 1.33 X 103 29.4* 1.97* 7.80
Tetrachloro-phthalic 2vol n-Heptane Q
+ lvol ether 60 3450 0.91 X 103 15.8 1.83Anhydride ft 30 3450 0.91 X 103 21.8 1.86 2.36
II tl 20* 3450 0.91 X 10 25.0* 1.89* 4.90
Tetrabromo-phthalic 3Anhydride n-Heptane 34 3600 1 X 103 10.02 1.41
II ii 20 3600 1 X 10^ 12.88 1.48 2.68 4.10It ■I 6 1 X 10 16.20 1.55
coCO
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
TABLE III
(continued)
AcceptorTemp.
Solvent °C Ec Kx- A f
Kcal/mole- A h
Kcal/mole- Ase .u.
Tetraiodo-phthalic Chloroform 20 3 36.20 2.10
Anhydride •• 31 3900 0.42 x 103 20.00 1.82n 15 3900 0.42 x 103 50.00 2.22 10.8 29.60
Naphthalene sym-TNB in n-CyH^g, and (d) Naphthalene-Chloranil in
(1 vol. CHCI3 + 3 vol. n-CyH^g).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
CM O CO <0 ^ CM « • • • • •— O o o o£-01 X 1 N 3 IJ J 3 0 0 NOIldMOSey WVIOW
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
0*0
3 7
Figure 4
Plot of molar absorption coefficient Ec vs. peak wave length of
the C-T band. (1) corresponds to Naphthalene TCPA, (2) to Naphthalene
TBPA, and (3) to Naphthalene TIPA. (Solvent: Chloroform).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
ofO«•
o o«•
oto
T"o nrmo oo
£-01*1N3I0UJ3OD NOIlddOSQV UV1OW
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
WAVE
LE
NGTH
(m
/*)
3 8
Figure 5
Plot of stability constants vs. peak wave length of the C-T bands
of the Naphthalene complexes in chloroform solution. The too-far-off
point corresponds to Naphthalene 2, 4, 7 TN-Fluorenone complex.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
"IO
o
S1NV1SN00 A11118 VIS
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
39
Figure 6
The C-T spectrum of Naphthalene-2, 4, 7 TN-Fluorenone complex
at three different temperatures. The curves from top to bottom corre
spond to (a)*— 6°C, (b) ~ 32°C, and (c) 55°C.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
OPT
ICA
L D
EN
SIT
Y
OS
0.8
07
0 6
Q 2
Q O 350 400 500450
WAVE L E N G T H (m/x)
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
CHAPTER B
INTERSYSTEM CROSSING IN CHARGE-TRANSFER COMPLEXES OF NAPHTHALENE WITH HEAVY ATOM CONTAINING ACCEPTORS
Introduction
Molecular perturbation of the triplet states has been the
subject of considerable discussion in the literature. McClure showed
that T-S emissions in Halobenzenes and Halonaphthalenes increase rapidly
with increasing atomic number of the substituents.''" Collisional spin-
orbital coupling has been invoked by Kasha in order to explain the T-S2enhancement of ^-Chloronaphthalene in a mixture with Ethyliodide. The
above explanation has been questioned in a recent work on the Phosphores
cence lifetime of p(-Halogenated Naphthalenes in Propylhalide solvents at
77°K. The lifetimes were found to decrease as the spin-orbital coupling
factors of either the external or internal Halogen increased. This effect
at low temperature is not compatible with a collisional explanation.
Evans studied the influence of paramagnetic molecules NO, O2 on
the absorption spectra of some aromatic hydrocarbons. He observed a
■*!). S. McClure, JT. Chem. Phvs., 17, 905 (1949).2Kasha, cit.
^S. P. McGlynn, M. J. Reynolds, G. W. Daigre and N. D. Christodouleas, Phosphorescence Spectra and Lifetimes of Externally Perturbed Naphthalenes and 0 (-Monoha1ogenated Naphthalenes. To be published.
40
R ep ro d u ced with p erm issio n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
4 1
number of weak absorption bands presumably attributable to the forbidden 4T-S transitions. Evans explained this phenomenon by means of spin-
orbital perturbation caused by the inhomogeneous magnetic field of the
paramagnetic molecule. It can be shown, however, that the effect of the
magnetic field on the breakdown of the spin selection rules is not suffi
cient to explain the strong enhancement of T-S absorption.^ It is worth
mentioning that the same phenomenon has been explained by Hoijtink in
terms of exchange interaction between the singlet and triplet states in6 7the presence of paramagnetic molecule. Finally Tsubomura, Mulliken
gand Murrell have indicated that the T-S absorption bands of various
aromatic donors induced by oxygen is the result of interaction between
the singlet excited state and the triplet of the aromatic through the
C-T state of the complex. The purpose of this work was to investigate
how the relative Phosphorescence to Fluorescence yield of Naphthalene
varies by complexing it and to illuminate the possible mechanism of
energy transfer.
Experimental
The Naphthalene used was a B.D.H. microanalytical reagent which
was purified by several recrystallizations from ether. The effectiveness
of this procedure was checked by further purification of the Naphthalene
^D. F. Evans, J. Chem. Soc., _7.» 1315 (1957).
■’Tsubomura and Mulliken, pp. cit.
^Hoijtink, pp. cit.
■^Tsubomura and Mulliken, pp. cit.gMurrell, op. cit.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
4 2
by zone refining. There was no detectable difference in the emission
spectrum of these two products, and this demonstrated the fact that the
recrystallization was a satisfactory purification process for this
product. The sym-TNB, Tetraiodophthalic anhydride were Eastman Kodak
products and the Tetrachlorophthalic anhydride was a Matheson Coleman
and Bell product. All these reagents were purified by several recrystal
lizations from ether. The solvent used was a mixture of ethyl ether:
isopentane 1:1 by volume (usually called EP).
The purification of ether involved reflux over sodium wire (or
safe sodium) for about 10 hours and subsequent distillation. This was
done no earlier than 2-3 days before the actual use in the spectrometry.
Isopentane was purified by reflux over sodium wire for about 10 hours,
distillation and passing through a column of activated silica. The EP
solvent forms a glass at low temperature, but because of the small
solubility of Tetrachlorophthalic anhydride, etc. in it, we had to
weigh small amounts of material resulting in greater inaccuracy of our
concentration values.
The total emission spectra was taken by means of a medium quartz
spectrograph using Kodak 103 (a) F and 103-F plates. The excitation
light derived from a general electric AH 6 mercury lamp and was filtered
in such a manner that only radiation between 2400-3000 A was transmitted.
(Combination of liquid filter of 120 gm. NiS04-6H20 + 22.5 gm. CoSO^-97H2O in a 10 cm. length path with Corning glass filter no. 9863) The
plates were traced in a Leeds and Northrup densitometer. All absorption
9M. Kasha, J. Opt. Soc., 38, 929 (1948).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
4 3
spectra were measured on a Beckman DK recording spectrophotometer. An
additional Beckman thermostatic control was used. The equilibrium
constants were determined using a Benesi-Hildebrand procedure.
Results
Naphthalene was used because of its favorable emission charac
teristics (large S-T separation -- 10,000 cm \ sharp and character
istic pattern of T-S emission at low temperatures), and the fact that
Naphthalene forms characteristic 1-1 change-transfer complexes with sym-
TNB and Tetrahalophthalic anhydrides. A difficulty, however, arose from
the fact that the absorption region of these complexes falls partly on
the Fluorescence region of Naphthalene. (See Figure 7.)
As a measure of triplet-singlet perturbation the ratio, intensity
of Phosphorescence/intensity of Fluorescence, for two selected peaks of
Phosphorescence and Fluorescence was taken. Radiatiort fcess deactivation
to the ground state should not be ignored as a supplementary factor for
the determination of the absolute quantum yields of Phosphorescence and
Fluorescence. These absolute quantum yields would be the safest crite
rion of triplet-singlet mixing, but the experimental conditions of this
work restricted us to the use of Phosphorescence yield relative to
Fluorescence yield. Nevertheless, it seems unlikely that these two
ratios very widely.
Another way of expressing relative yields would be the ratio of
the areas under the Phosphorescence and Fluorescence curves, respec
tively. However, the partial overlap of the Fluorescence spectrum of
Naphthalene with the absorption spectra of the selected acceptors dimin
ished its reliability as an accurate expression of relative quantum
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
4 4
yields.
The problem was examined in two steps:
A. Proof of the enhancement of singlet-triplet perturbation of
Naphthalene on account of complex formation. This is easily done by
comparison of the total emission spectra of Naphthalene with that of
anyone of its complexes. (See Figure 8 .)
B. Investigation of the extent of perturbation as a function of
(1) the concentration of the acceptor and (2) its kind.
Intensity of Phosphorescence &(1) Dependence of Intensity of Fluorescence = ^ f on the
concentration of the acceptor. The total emission spectra of three
solutions of Naphthalene with different amounts of Tetrachlorophthalic
anhydride are shown in Figure 9. The .. ratios at the different
concentrations of Tetrachlorophthalic anhydride (TCPA) or the ratios of
C tcpa /concentration ^Naphthalene a^e given in Table IV. The values of < Pp
and are obtained from the heights of chosen peaks of Phosphorescence
and Fluorescence translated into intensities. For example, the
Fluorescence intensity at 28000 cm”'*' compared with the Phosphorescence
intensity at 19880 cm in the three solutions.
This choice came out as a compromise of two facts: (A) the over
lap of Fluorescence with the absorption of acceptor (Figure 7) and (B)
the variation of the sensitivity of the plate with the exposure (H-D
curve). We tried to compare such bands of Fluorescence as those which
do not overlap with the absorption spectrum of the acceptor on the one
hand and fall on the linear portion of H-D curve on the other. Such
data are given in Table IV. The corresponding plots of vs.
concentration of TCPA are shown in Figure 10. Tables V, VI and VII
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
4 5
refer to TBPA, TIPA and sym-TNB complexes, respectively. A plot analo
gous to the plot of Figure 10 is given in Figure 11 for the Naphthalene-
TBPA complex.
tration of the complex. These diagrams exhibit an upward deviation from
the straight line. It is not unlikely that, in addition to absorption
of Fluorescence by the acceptor component, static quenching of Fluores
cence due to complex formation is responsible for the relative decrease
of Fluorescence,
Regarding the absolute values of concentration of the acceptors,
we should mention that these are approximate because the weighing of
very small amounts of materials (these compounds are almost insoluble
in the solvent mixture) introduced appreciable inaccuracy. However,
the relative concentrations are more or less accurate since dilution of
the solutions introduce small errors.
total emission spectra of Naphthalene with equimolecular amounts of
Eq. 6 shows that the condition that favored 4 , namely having < d' small
compared with ^a' militates against 4 . Consequently, one should expect
4 to increase from TCPA to TIPA complex in the Tetrahalophthalic anhy
dride series. In addition, — — changes in the same direction. It is,
therefore, reasonable to conclude that the triplet- (C-T) state mixing
probability increases from TCPA to TIPA. This agrees quite well with the
experimentally observed changes at ^ p / ^ f in these complexes.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
5 0
In the above discussion the strong dependence of the enhancement
of singlet-triplet transition probability on the atomic number of the
heavy atom of the acceptor molecule is not expressed in a clearcut and
direct manner. This is a serious drawback of the theory, which can rea-
complex, in view of the fact that spin-orbit perturbation is not expected
in this complex; but it does not anticipate directly any heavy atom effect.
It may be that this theory requires some further improvement to include
the heavy atom effect or that in case of heavy atom containing acceptor,
the spin-orbital perturbation mechanism acquires predominant role. We
believe that the second is the case. In the complexes with non-heavy
atom containing acceptors the increase of the ratio of 4>P/ f is due
to the transfer of energy from the singlet excited state to the lowest
triplet state through the C-T level, since direct singlet-triplet mixing
heavy atoms are involved the direct interaction between the excited
singlet and the lowest triplet becomes important and the extent to which
singlet-triplet mixing occurs is proportional to the amount of complex
formed since such an interaction requires small distance between the
"optical" molecule (donor) and perturbing molecule. In other words
we consider complex formation as a "localistic" prerequisite of the
Z-effeet.
s onably Naphthalene-TNB
is not sufficient to explain the enhancement13,14
by Tsubomurct, Mulliken and Murrell. 5 In
shown
In complexes, however, where
13Tsubomura, and Mulliken, ££. cit.14Murrell, op. cit.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
TABLE IV
FLUORESCENCE AND PHOSPHORESCENCE INTENSITIES IN THE TOTAL EMISSION SPECTRA OF NAPHTHALENE-TCPA COMPLEX
1 2 3 4 5 6 7 8
C tcpain m /C xlO
j t> r>*-*19880
cm"-*-V*-*28000
cm"1V*-*285 00 cm"-*-
_Z'^28890cm"-*-
2.3 0.67 0.03 0.05 0.08 22.10 13.4 8.40
0.76 0.65 0.10 0.22 0.28 6.50 2.92 2.30
0.19 0.42 0.26 0.43 0.51 1.61 1.00 0.82
NOTE: The symbols and designate Phosphorescence and Fluorescence intensities at theapproximate frequencies indicated. ^"Naphthalene 0.6 x 10" m/-C .
5 2
TABLE V
FLUORESCENCE AND PHOSPHORESCENCE INTENSITIES IN THE TOTAL EMISSION SPECTRA OF NAPHTHALENE-TBPA SYSTEM
1 2 3 4 5 6
C tbpain m (C xlO
T -+ 18^70 cm
31630cm” -
H x
>*--*31270cm""
0.46 0.25 0.20 0.33 1.25 0.76
0.15 0.15 0.35 0.55 0.43 0.27
0.04 0.15 0.64 0.82 0.23 0.18
NOTE: The symbols have the same meaning as in Table IV.Naphthalene ~ 0.6 x 10”2 n / £ .
R ep ro d u ced with p erm issio n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
5 3
TABLE VI
FLUORESCENCE AND PHOSPHORESCENCE INTENSITIES IN THE TOTAL EMISSION SPECTRA OF NAPHTHALENE-TIPA COMPLEX
1 2 3 4 5 6
(Ttipain m /•£ xlO3
>*■-*•19880 cm-1
If*-* 28500 cm"
V" "*28890 cm"'*-
4 ^ / d f ,
0.23 0.36 0.25 0.39 1.44 0.92
0.06 0.06 0.28 0.35 0.21 0.17
NOTE: The symbols Y V and y f have the same meaning as inthe previous table. CNaphthalene 0.62 x 10“ m/ £ .
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
5 4
TABLE VII
FLUORESCENCE AND PHOSPHORESCENCE INTENSITIES IN THE TOTAL EMISSION SPECTRA OF NAPHTHALENE SYM-TNB
1 2 3 4 5 6
^sym-TNB in m/ x 104
£•-*21300cm"l
■ -*28000cm“l
T>-*28500cm“^
4 r l< h 5
1.0 0.23 0.78 0.83 0.29 0.28
7.3 0.23 0.69 0.78 0.33 0.30
NOTE: The only difference here is that C*Naphthalene isdifferent in the two solutions. ^Naphthalene = 5 x 10” m/ and 10 x 10“ m / €* for the first and second solutions respectively.
R ep ro d u ced with p erm iss io n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
5 5
TABLE VIII
COMPARISON OF FLUORESCENCE AND PHOSPHORESCENCE INTENSITIES IN THE TOTAL EMISSION SPECTRA OF NAPHTHALENE WITH TCPA, TBPA AND TIPA
1 2 3 4
Comp lex of Naphthalene with
f a21300cm"l
H29400cm--*-
f a / f a
TCPA 0.20 0.40 0.50
TBPA 0.19 0.29 0.64
TIPA 0.46 0.35 1.32
NOTE: The intensities of Phosphorescence and Fluorescence atthe frequencies indicated as well as their ratio ( p ^ l t p t are recorded. Cone, of Naphthalene c^0.77 x 10” m/^ . Cone, of acceptors 0.58x 10"4 r a /£ .
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
Figure 7
Molar absorption coefficients (Era) of (1) Naphthalene in iso
octane, (2) TCPA in chloroform, and (3) Naphthalene-TCPA in chloroform,
(y = 1 for Naphthalene; y = 2.7 for TCPA, and Y = 2 for Naphthalene-
TCPA.)
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
CM
X
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
WAVE
NU
MBE
RS,
CM*
xl(T
57
Figure 8
Total emission spectra of (A.) pure Naphthalene and (B)
Naphthalene-sym-TNB complex. The wave number scale has been dis
continued in the blackening vacuum between 28000 cm and 24000 cm
Exposure times: 60 minutes.
R ep ro d u ced with p erm iss io n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
PLAT
E
BO
60
-30
2024 2332 30 29 26
WAVE NUMBERS, CM"* xlO*
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm ission .
58
Figure 9
Total emission spectra of 3 solutions of Naphthalene complex.
Naphthalene is of the order of 10"^ m/^ in all cases. C tCPA is
of the order of 10 ^ m I t in (A) and then in (B) and (C) is 3 and 4
times smaller respectively. The dotted lines in the right of each
diagram separate the emission of the pure TCPA from the phosphorescence
of Naphthalene.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
PLAT
E BL
ACKE
NNG,
OQ
- t o
IIII <0 Itt4 ttIt tlM to tt
WAVE NUMBERS CM*' xIO’*
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
59
Figure 10
cm
r *Plot of 4 > t vs. I—TCPA. (p p corresponds to 19880
1 approximately. ( f fc2 and 3 (from toP to bottom)
correspond to 28000, 28500, and 28890 cm"1 respectively.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
jfcp4>f 2520
OozoIDzH5HOZ
IX
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
Plot of
approximately.
31630 and 31270
Figure 11
r a -ivs. LTBPA. <^p corresponds to 18570 cm
( f t S-\ and (from top to bottom) corresponds to
cm respectively.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
- »
- CM
001
d<J)
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm ission .
CON
CEN
TRA
TIO
N
(M/L
) x
IO4
6 1
Figure 12
Total emission spectra of Naphthalene with equimolecular amounts
of (A) TIPA, (B) TBPA, and (C) TGPA. The curves in the right represent
the overlapping emissions of the acceptors with the phosphorescence of
pure naphthalene. (Compare with Figure 8 .)
R ep ro d u ced with p erm issio n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
WAVE NUMBERS, CM'1 x 10
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
6 2
Figure 13
^ p / 4% vs. (Spin-orbital coupling factor)^ of £ £ , Br, and I.
^ p and ^ correspond approximately to 21300 and 29400 cm
respectively.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
r *>
rcM
s-oo z
d<j>
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm ission .
(so
cf
)
6 3
Addendum
For a verification of the results obtained on the medium quartz
spectrograph, we measured the total emission spectra of three additional
Tetrachlorophthalic anhydride and (c) Phenanthrene-sym-TNB on an Aminco-
Keirs Spectrophotometer. In this instrument a Xenon lamp is used as an
excitation source and the emitted light is separated from the excitation
light by means of two grating monochromators (excitation and emission)
and a system of five slits the width if which can be adjusted at will
from 0.5 mm to 5 mm. Of course, a phosphoroscope can be used in case
that only Phosphorescence is investigated. A photomultiplier tube
(IP 28) connected with an Aminco Spectrophotometer and a X-Y recorder
was used as a detecting, measuring and recording device.
The materials were:
(1) Acenaphthene (Matheson Coleman and Bell product) recrystal
lized from ether and zone refined.
(2) Phenanthrene -- very pure sample graciously sent by B. D.
Blaustein of the U. S. Bureau of Mines.
(3) sym-TNB and Tetrachlorophthalic anhydride. The source and
method of purification have been described in the main part.
The solvents used were ether:isopentane (1:1) for the Acenaphthene
complexes and methylcychohexane:isopentane (1:1) mixtures. The results
are similar to those obtained by using medium quartz spectrograph and
are indicated in Tables IX, X and XI. Figure 14 shows how the total
emission spectra of Phenanthrene-sym-TNB system in the three solutions
(A, B, C) look, if we reduce the relative intensities in such a way that
the Fluorescence spectra have the same area approximately.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
6 4
TABLE IX
RELATIVE FLUORESCENCE AND PHOSPHORESCENCE INTENSITIES OF ACENAPHTHENE- TCPA MEASURED WITH THE AMINCO-KEIRS SPECTROPHOTOMETER
^Acceptor <t?fi 4 , 4 > sSolution £Donor 470 m fA- 315m fc 330m/*. 4 > i, 4 k
A Acenaphthene 0.126 15.9 26.2 0.008 0.005
B 1 0.310 9.9 14.4 0.035 0.021
C 2 0.850 5.7 8.0 0.149 0.106
D 10 1.65 3.0 4.0 0.550 0.412
NOTE: Table IX shows the relative intensity of Phosphorescenceand Fluorescence (arbitrary units) of Acenaphthene-Tetrachlorophthalic anhydride system. Column (1) indicates the ratio of concentration of
^Acceptoracceptor and donor. The value 1 corresponds to (^Donor ' ’10~4 m!<.7.5 x 10“4 m/-£ . Only the concentration of donor varies in these solutions.
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
6 5
TABLE X
RELATIVE FLUORESCENCE AND PHOSPHORESCENCE INTENSITIES OF ACENAPHTHENE- SYM-TNB MEASURED WITH THE AMINCO-KEIRS SPECTROPHOTOMETER
^Acceptor 4>»Solution £Donor 525m f* 325m 340m
B 1.0 6.0 73 91 0.08 0.07
C 2.5 9.0 37 37 0.24 0.24
D 5.0 11.0 35 31 0.31 0.35
NOTE: The intensity units are arbitrary. The variable concentrate. ^ 6.2 xl0~3 m f t
tion is that of acceptor i 0.6 xl0“4 n/^
R ep ro d u ced with p erm issio n o f th e cop yrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
66
TABLE XI
RELATIVE FLUORESCENCE AND PHOSPHORESCENCE INTENSITIES OF PHENANTHRENE- SYM-TNB COMPLEX MEASURED WITH THE AMINCO-KEIRS SPECTROPHOTOMETER
R ep ro d u ced with p erm issio n o f th e copyrigh t ow ner. Further reproduction prohibited w ithout p erm issio n .
0S£OQfrNOIlddOSflV #(r/ui) xouiy
009
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm ission .
500
550
600
650
700
Xm
axtm
^),
EMIS
SIO
N
Reproduced with permission of the copyright owner. Further reproduction prohibited without permission.
TABLE XII
COMPARISON OF ^MAX (ABSORPTION) AND ^MAX (EMISSION) FOR SOME C-T COMPLEXES
ComplexAbsorption ^max (mh)
Emission ^Imax (mfO
Absorption* X max (m|-0
Emission* X max (mK)
Anthracene-sym-TNB 440 575 450 590
Anthracene-TCPA 420 550 430 555)
Anthracene 2, 4, 7 TN Fluorenone 500 670 550 685
Phenanthrene-sym-TNB 365 510 390 545
Tetraphene-sym-TNB 425 575 - -
3,4 Benzotetraphene-sym-TNB 400 500 - -
Coronene-sym-TNB 415 545 - =
NOTE: Table XII shows the peak wave lengths of absorption and emissionbands of some C-T complexes. *Czekalla's results.
00
BIBLIOGRAPHY
Bayliss, N. S. "Spectra of Iodine and Bromine Solutions," Nature,163, 764 (1949).
Benesi, H. A. and Hildebrand, J. H. "A Spectrophotometric Investigation of the Interaction of Iodine with Aromatic Hydrocarbons," J. Am. Chem. Soc., 71, 2703 (1949).
Bier, A. and Ketelaar, J. A. "The Relation Between, the Emission and Absorption Spectra of Molecular Compounds of sym-Trinitobenzene,"Rec. tray, chim., 73, 264 (1954).
Bier, A. "Complexes of Aromatic Nitrocompounds," Rec. trav. chim., 75, 866 (1956).
Blake, N. W., Winston, H. and Patterson, J. A. "Complexes of Naphthalene with Iodine and Bromine. On the Origin of the Spectra Between Halogene and Aromatics," _J. Am. Chem. Soc., J 3 , 4437 (1951).
i t i iBriegleb, G. Zwischenmolekulare Krafte. Karlsruhe, Germany: G. Braun,
1949.
Cunningham, K. J., Dawson, W. and Spring, F. S. "Microdetermination of the Molecular Weights of Picrates by a Spectrophotometric Method,"J. Chem. Soc., 2305 (1951).
Czekalla, J., Briegleb, G., Herre, W. and Glier, R. "Fluoreszenz-und Absorptionspektren von Molekulverbindungen bei tiefen Temperaturen. Energieubergange in Molekuverbindungen," Z. Elektrochem., 61, 537 (1957).
Czekalla, J., Schmillen, A. and Mager, K. J. "Fluoreszenespectren,Reflexionspectren und Fluoreszenzabklingzeiten von Kristallinen Molekulverbindungen," Z. Elektrochem., 63, 623 (1959).
Evans, D. F. "Perturbation of Singlet-Triplet Transitions of Aromatic Molecules by Oxygen Under Pressure," J[. Chem. Soc., 1351 (1957).
Feigl, F. Spot Tests in Organic Analysis. 5th Edition. New York: Elsevier Publishing Company, 1958.
Good, M., Major, A., Nag-Chaudhuri, J. and Me Glynn, S. P. "Iodine Complexes of Ethyl Mercaptans, Diethyl Sulfide and Diethyl Disulfide," J. Am. Chem. Soc., 83, 4329 (1961).
82
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
8 3
Ham, J. S., Platt, J. R. and McConnell, H. "The Ultraviolet Spectra of Benzene-Halogen Complexes and of Iodine in Solutions," J. Chem. Phys., 19, 1301 (1951).
Hastings, S. H., Franklin, J. L., Schiller, J. C. and Matsen, F. A. "Molecular Complexes Involving Iodine," J. Am. Chem. Soc., 75,2900 (1953).
Hoijtink, G. J. "The Influence of Paramagnetic Molecules on Singlet- Triplet Transitions," J. Mol. Phys., J3, 67 (1960).
Kasha, M. "Transmission Filters for the Ultraviolet, " J- ■ s oc., 71, 2703 (1949).
Kasha, M. "Collisional Perturbation of Spin-Orbital Coupling and the Mechanism of Fluorescence Quenching," J. Chem. Phys., 20, 71 (1949).
Kramers, H. A. Die Grundlagen der Quantum Theorie. Akademische Verlagsgesellshaft M.B.H., 1938.
Lewis, G. N. and Kasha, M. "Phosphorescence and the Triplet State,"J. Am. Chem. Soc., 66, 2100 (1944).
McClure, D. S. "Triplet-Singlet Transitions in Organic Molecules.Lifetimes Measurements of the Triplet State," J. Chem. Phys., 17,905 (1949).
McClure, D. S. "Selection Rules for Singlet-Triplet Perturbation in Polyatomic Molecules," J_. Chem. Phys., 17, 665 (1949).
McClure, D. S. "Electronic Structure of Transition-Metal Complex Ions," Rad. Research Suppl., 2, 218 (1960).
McConnell, H., Ham, J. S. and Platt, J. R. "Regularities in the Spectra of Molecular Complexes," J. Chem. Phys., 21, 66 (1953).
McGlynn, S. P. and Boggus, J. D. "Energy Transfer in Molecular Complexes of sym-Trinitrobenzenes with Polyacenes," J. Am. Chem. Soc., 80,5096 (1958).
McGlynn, S. P. "Energetics of Molecular Complexes," Chem. Revs., 58,1113 (1958).
McGlynn, S. P., Reynolds, M. J., Daigre, G. W. and Christodouleas, N. D. "Phosphorescence Spectra and Lifetimes of Externally Perturbed Naphthalenes and O^-Monohalogenated Naphthalenes," To Be Published.
Moodie, M. M. and Reid, C. "Lowest Triplet State of Anthracene,"J. Chem. Phys., 22, 252 (1954).
Mulliken, R. S. "Structures of Complexes Formed by Halogen Molecules with Aromatic and Oxygenated Solvents," J. Am. Chem. Soc., 72, 600 (1950).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
8 4
Mulliken, R. S. "Overlap Integrals and Chemical Bonding," _J. Am. Chem. Soc.,_72, 4493 (1950).
Mulliken, R. S. "Lewis Acids and Bases and Molecular Complexes," J.Chem. Phys., 19, 514 (1951).
Mulliken, R. S. "Molecular Complexes and Their Spectra," J. Am. Chem. Soc., 74, 811 (1952).
Mulliken, R. S. "Forces Intermoleculaires de Transfer de Charge,"J. Chim. Phys., 51, 341 (1954).
Mulliken, R. S. "Molecular Compounds and Their Spectra. Orientation inMolecular Complexes," J. Chem. Phys., 23, 397 (1955).
Mulliken, R. S. "Molecular Compounds and Their Spectra. Some Problemsand New Developments," Rec.trav. chim., 75, 845 (1956).
Murrell, J. N. "Molecular Complexes and Spectra. The Relationship Between the Stability of the Complex and the Intensity of the Charge-Transfer Band," J. Am. Chem. Soc., 81, 5037 (1949).
Murrell, J. N. "The Effect of Paramagnetic Molecules on the Intensity of Spin-Forbidden Absorption Bands of Aromatic Molecules," J. Mol. Phys., 3, 319 (1960).
Murrell, J. N. "The Theory of Charge-Transfer Spectra," Quart. Revs.,XV, 191 (1961).
Nakamoto, K. "Peculiarity of Dichroism of Aromatic Molecular Compounds, The Dichroism of Quinhydrone, sym-Trinitrobenzene and Related Compounds," J. Am. Chem. Soc., 74, 1739 (1952).
Nagakura, S. "Molecular Complexes and Their Spectra. VII. TheMolecular Complexes Between Iodine and Triethylamine," J. Am. Chem. Soc., 80, 520 (1951).
Orgel, L. E. and Mulliken, R. S. "Molecular Complexes and Their Spectra. The Spectrophotometric Study of Molecular Complexes in Solution; Contact Charge-Transfer Spectra," J. Am. Chem. Soc., 79, 4839 (1957).
Padhye, M. R., McGlynn, S. P. and Kasha, M. "Lowest Triplet Level of Polyacenes," J. Chem. Phys., 24, 588 (1956).
IIPfeiffer, P. Organische Molekulverbindungen. 2nd Edition. Stuttgart,
Ferdinand Enke Germany (1927).
Reid, C. "Inter-and Intra-Molecular Energy Transfer Processes. Nitrocompounds and Hydrocarbons," J. Chem. Phys■, 20, 1212 (1952).
Sheinker, Yu. N. and Golovner, B. M. Izvest. Akad. Nauk. j5. S. R. ser. Fiz., 17, 681 (1953).
R ep ro d u ced with p erm iss io n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
85
Siele, V. I. and Picard, J. B. "Spectrophotometric Determination of Molecular Weights by Use of Styphnates and Picrates," Appl. Spectroscopy 12, 8 (1949).
Tsubomura, H. and Mulliken, R. S. "Molecular Compounds and Their Spectra. Ultraviolet Absorption Spectra Caused by the Interaction of Oxygen with Organic Molecules," J. Am. Chem. Soc., 82, 5966 (1952).
iiWeitz-Halle, E. "Zur Theorie der Chinhydrone," Z. Elektrochem., 34,538 (1928).
Weitz, E. "Radikale, Quasi-Radikale, merichinoid Verbindungen und Chinhydrone," Angew. Chem., jjfi, 658 (1954).
Weiss, J. "The Formation and Structure of Some Organic Molecular Compounds," J. Chem. Soc., 245 (1952).
Woodward, R. B. "The Mechanism of Diels-Alder Reaction," J. Am. Chem. Soc., 64, 3058 (1942).
Yuster, P. and Weissman, S. I. "Effect of Perturbation on Phosphorescence; Luminescence of Metal Organic Complexes," J. Chem. Phys.,27, 1182 (1949).
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
VITA
Nicholas D. Ghristodouleas was born in Proselion (Kalamata),
Greece on August 4, 1932.
He received his high school education in Kalamata. In November
1951 he entered the Chemistry School of the University of Athens
(Greece) and received his B.S. degree in February 1956.
In January 1959 after serving for two years in the Greek Army,
he was admitted to the Graduate School of Louisiana State University.
He is now a candidate for the degree of Doctor of Philosophy.
86
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .
EXAMINATION AND THESIS REPORT
Candidate: Nicholas D. Christodouleas
Major Field: Chemistry
Title of Thesis: Intersystem Crossing and Energy Transfer in Charge Transfer Complexes
Approved:
& O vicCl.Major Profes§p/and/Chilairman
Dean of the Graduate School
E X A M I N I N G COMMITTEE:
Date of Examination: July 17 > 1962
R ep ro d u ced with p erm issio n o f th e copyrigh t ow n er. Further reproduction prohibited w ithout p erm issio n .